Mechanisms of vegetation-induced channel narrowing of an unregulated canyon river: Results from a natural field-scale experiment
Mechanisms of vegetation-induced channel narrowing of an unregulated canyon river: Results from a natural field-scale experiment
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DOI：
10.1016/j.geomorph.2013.12.033
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发表时间：
2014-04
期刊：
影响因子：
3.9
通讯作者：
R. Manners;J. Schmidt;M. Scott
中科院分区：
文献类型：
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作者：
R. Manners;J. Schmidt;M. Scott
位于科罗拉多州西部Yampa峡谷的Yampa河下游是一项自然的田野规模的实验，始于入侵的河岸植物Tamarisk(Tamarixspp.)在一条未受管制的河流上殖民。为了应对罗望鱼的快速入侵，自1961年以来，该海峡在最宽的河段缩小了6%。利用这一独特的环境，我们重建了地貌和植被的历史，以确定在没有其他环境扰动的情况下，植被改变河流过程从而导致河道变窄的关键机制。从我们的重建中，我们发现罗望子入侵和频道改变的时间和大小有明显的相似性，尽管频道反应滞后，因此表明罗望子是驱动力。在建立的十年内，罗望子有效地捕获了沉积物，因此提高了泛滥平原的建设速度。随着时间的推移，增加罗望子的覆盖率也减少了洪泛区剥离的发生。罗望子的补充是由水文和水力变量驱动的，大多数(84%)罗望子植物在两年洪水的阶段之前建立。因此，在建立时，几乎所有的植物都会定期与水流和泥沙输运场相互作用。我们的分析是基于这样的假设，即Yampa河的流态是静止的，只有河岸植被群落发生了变化。虽然没有受到水资源开发的严重影响，但我们确定水流状况的某些方面已经发生了变化。然而，这一转变涉及极端潮湿和干旱年份的聚集，并没有直接影响河流过程。相反，这些变化直接影响了河岸植被，植被覆盖的变化反过来又改变了河流的过程。如今，渠道改变和新罗望鱼招募的速度很小。我们认为，罗望子河的迅速扩张和相关的滩地建设导致河道变窄，使扬帕河进入了一种新的稳定状态，其特点是河道相对静止。
The lower Yampa River in Yampa Canyon, western Colorado serves as a natural, field-scale experiment, initiated when the invasive riparian plant, tamarisk (Tamarixspp.), colonized an unregulated river. In response to tamarisk's rapid invasion, the channel narrowed by 6% in the widest reaches since 1961. Taking advantage of this unique setting, we reconstructed the geomorphic and vegetation history in order to identify the key mechanisms for which, in the absence of other environmental perturbations, vegetation alters fluvial processes that result in a narrower channel. From our reconstruction, we identified a distinct similarity in the timing and magnitude of tamarisk encroachment and channel change, albeit with a lag in the channel response, thus suggesting tamarisk as the driving force. Within a decade of establishment, tamarisk effectively trapped sediment and, as a result, increased floodplain construction rates. Increasing tamarisk coverage over time also reduced the occurrence of floodplain stripping. Tamarisk recruitment was driven by both hydrologic and hydraulic variables, and the majority of tamarisk plants (84%) established below the stage of the 2-year flood. Thus, upon establishment nearly all plants regularly interact with the flow and sediment transport field. Our analyses were predicated on the hypothesis that the flow regime of the Yampa River was stationary, and that only the riparian vegetation community had changed. While not heavily impacted by water development, we determined that some aspects of the flow regime have shifted. However, this shift, which involved the clustering in time of extremely wet and dry years, did not influence fluvial processes directly. Instead these changes directly impacted riparian vegetation and changes in vegetation cover, in turn, altered fluvial processes. Today, the rate of channel change and new tamarisk recruitment is small. We believe that the rapid expansion of tamarisk and related floodplain construction that led to a narrower channel pushed the Yampa River into a new stable state, characterized by a relatively static channel.